Multi-layer, flexible transfer tape

ABSTRACT

Multi-layer flexible transfer tapes are provided which are useful for covering printing or typing errors in texts or drawings so that corrections may be made. The transfer tapes are characterized by the inclusion of two binder-containing pigmented transfer layers, wherein one transfer layer is cationic and the other transfer layer is anionic.

FIELD OF THE INVENTION

This invention relates to a multilayer flexible transfer tape comprisinga backing and a layer of pressure-sensitive adhesive, at least onebinder-containing pigmented transfer layer being present between thebacking and the layer of pressure-sensitive adhesive and showing greateradhesion to the layer of pressure-sensitive adhesive than to thebacking.

BACKGROUND OF THE INVENTION

A transfer tape of the type described above is known, for example, fromDE 196 17 850 C1. This document describes a transfer tape in which apigmented, particularly white-pigmented, transfer layer, then anotherpigmented transfer layer containing a non-white pigment and finally thelayer of contact adhesive are arranged on a conventional backing. Thistape is particularly effective in covering the transfer layer withoutany significant loss of “whiteness”. The known tape is advantageouslyused in roll form in hand-held “rollers” so that the transfer layer canbe applied simply, quickly and uniformly to a substrate in order tocover printing/typing errors in texts or drawings so that correctionsmay be made. The transfer layer applied can then be written on, forexample with a fountain pen or ball-point pen. In some cases, it hasbeen found in connection with such corrections that the dyes in thelettering covered by the tape migrate to the surface of the coveringlayer applied, particularly under the influence of moisture, so that thecovered letting can be seen again.

SUMMARY OF THE INVENTION

Accordingly, the problem addressed by the present invention was tofurther develop the transfer tape mentioned at the beginning in such away that the “strike-through” of covered lettering would be eliminatedwithout any adverse effect on the desirable properties, particularly thecovering power of the transfer layer.

According to the invention, the solution to this problem ischaracterized in that the transfer tape comprises two binder-containingpigmented transfer layers, one of the pigmented transfer layers beingcationic and the other pigmented transfer layer being anionic.

DETAILED DESCRIPTION OF THE INVENTION

Advantageous embodiments of the present invention are defined in thesubsidiary claims. In these embodiments, the two transfer layers have athickness of about 5 to 25 g/m² and a total thickness of about 15 to 30g/m². The separate adhesive layer preferably has a thickness of about 1to 5 g/m² and more preferably in the range from about 2 to 4 g/m².Particularly good effects are obtained if a fine-particle metal powder,more particularly fine-particle aluminium, is present in the anionictransfer layer and/or in the adhesive layer. The fine-particle metalpowder is preferably present in the form of platelets. The platelet-likealuminium particles advantageously have a thickness of about 3 to 10 μmand a diameter of about 4 to 17 μm. The quantity of fine-particle metalpowder used is between about 0.1 and 3.5% by weight, based on theparticular dry layer. Particularly favorable effects are obtained if theanionic transfer layer is located between the cationic transfer layerand the adhesive layer. If the fine-particle metal powder is present inthe adhesive layer, the sequence of the anionic and cationic transferlayers is of no relevance. In individual cases, it is of particularadvantage if, as seen from the backing, the cationic transfer layer isapplied first, followed by an adhesive, anionic transfer layer with nofurther layer of pressure-sensitive adhesive, the adhesive anionictransfer layer in particular containing fine-particle metal, moreparticularly fine-particle aluminium.

The basic concept of the present invention is that, irrespective of thesequence in the layer structure of the transfer tape, the transfer tapecomprises a cationic and additionally an anionic transfer layer. Theterms “anionic” and “cationic” will readily be understood by the expert.The transfer layers are preferably prepared using binder dispersions,i.e. dispersions containing solid small polymer particles, moreparticularly in aqueous form. Commercially obtainable cationic andanionic aqueous dispersions may be used, for example cationic aqueousdispersions commercially obtainable as Acronal®) 280 KD (from BASF AG),Butonal® LS 170 K (from BASF AG), Jagotex® AL 2463 (from Jäger),cationic solutions obtainable, for example, as Worleecryl® (cationicpure acrylate solution, clear to slightly milky solution, on the onehand 25% in water (7712 W) and on the other hand 40% inwater/isopropanol (40:20) (7712), pH value 5 in either case) (fromWorlee Chemie GmbH, Hamburg) and anionic aqueous dispersions obtainableas Acronal® S 725 and S 726 (butyl acrylate/styrene copolymer) (fromBASF AG), as Acronal® V 205 (from BASF AG), as Styrofan® D 422 andPropiofan® 6D (from BASF AG). The activities mentioned are attributableto the particular surfactant used in the emulsion polymerizationprocess. In the case of an anionic dispersion, anionic surfactants acarboxyl group (—COO⁻) are used as stabilizers in the emulsionpolymerization. These groups face outwards from the dispersed polymerparticles. In the case of the cationic dispersions, cationic surfactantswhich almost without exception contain a quaternary ammonium ion(—N⁺(R₃)) as hydrophilic group are used in the emulsion polymerizationprocess. This information is all the expert needs to choose suitablecommercially available ionic aqueous dispersions for achieving theobjects of the invention. Reference is made in this connection to Dr. H.Stache “Tensid-Taschenbuch”, Carl Hanser Verlag München/Wien, 1979, pp.2/3 and Römpps Chemie-Lexikon, 7^(th) Edition, Georg Thieme Verlag,1992, Vol. 6, p. 4495, right-hand column to 4499, left-hand column.

Accordingly, the above-mentioned aqueous dispersions and solutions arepreferably used in the production of the transfer layers to be formed inaccordance with the invention. The above list of aqueousdispersions/solutions is by no means complete and, in particular, is notlimiting in regard to their choice. On the contrary, it is quite clearto the expert that other binders may also be used, especially since theessence of the invention does not lie in the type of binder used, butsolely in the cationic or anionic character of the transfer layer. Theconcentration of the binder in the dispersion is not critical. As arough guide, it may be between about 25 and 70% by weight and ispreferably between about 40 and 60% by weight. The aqueous dispersionfor forming the transfer layers is applied to the backing in a quantityof preferably about 15 to 35 g/m² (dry weight) and more preferably about18 to 25 g/m², this quantity representing the total quantity of bothtransfer layers, i.e. the cationic and anonic transfer layer.

Typical additives, for example foam inhibitors, wetting agents and thelike, may be used in the production of the various layers.

The layer of pressure-sensitive adhesive may consist of commerciallyavailable pressure-sensitive adhesives, for example theFreihoff-Dispersion VP 859/6. The above-described materials of theindividual layers of the transfer tape according to the inventiongenerally satisfy the basic requirement that the adhesive tensionbetween the backing and the transfer layers mentioned is lower thanbetween the transfer layers and the layer of pressure-sensitive adhesive(cf. DE 196 17 850 C1).

Technologically, the invention may be explained as follows: most of thedyes in writing fluids are synthetic dyes based on aromatic orheterocyclic compounds. The dyes are either ionic (for example allwater-soluble dyes) and nonionic compounds (for example dispersionsdyes). Among the ionic dyes, there are anionic and cationic types. Theanionic dyes have a negatively charged dye ion while the cationic dyeshave a positively charged dye ion so that, previously, a distinction wasgenerally drawn between acidic and basic dyes. It has been found that,irrespective of the particular type of lettering, i.e. whether itcontains an anionic or cationic dye, the present invention—in thecovering of a writing/printing error for example—enables the troublesomemigration of the dyes through the covering layer to be eliminated. Ifthe lettering contains an anionic dye, the cationic transfer layer ofthe transfer tape according to the invention blocks any migration. Inthe case of a cationic dye, this blocking effect is developed by theanionic covering layer (cationic dye binds to the anionic layer, etc.).Here, the dye does not migrate through the polymer itself, but throughmicrovoids present in the transfer layer. If the dye migrates throughthose voids, it automatically comes into contact with the active andoutwardly directed parts of the surfactants present on the surface ofthe polymer particles and is arrested by corresponding interaction.

The advantages obtainable through the invention may be summarized asfollows: the above-mentioned strike-through of covered lettering iseliminated in the required manner without any adverse effect on thedesirable properties or on the covering power of the transfer layer.Writing/printing can be permanently covered.

The invention is illustrated by the following Examples.

EXAMPLE 1

The following aqueous dispersions were prepared to form the variouslayers of the transfer tape according to the invention.

Dispersion for the Cationic Transfer Layer

Aqueous acrylate solution (25% in 35.0 parts by weightwater/Worleécryl ® 7712 W (Worleé Chemie GmbH, Hamburg) Water 15.3 partsby weight Alkylammonium salt of polycarboxylic acids 1.0 part by weight(Lactimon ® WS, Byk Chemie GmbH) Defoamer (hydrophilic silicone-likecomponents 0.2 part by weight in mineral oil) (Byk ® 034) Amorphoussilica (Syloid ® 244, Grace, USA) 5.0 parts by weight Titanium dioxide(rutile) (Finntitan RDD, 43.5 parts by weight Kemira, Finland) 100.0parts by weight

Dispersion for the Anionic Transfer Layer

Aqueous copolymer dispersion of n-butyl acrylate 36.0 parts by weightand styrene (45%) (Acronal ® S 725, BASF AG) Aqueous carboxyfunctionalacrylate copolymer 4.0 parts by weight (69%) (Acronal ® V 205, BASF AG)Aqueous polyvinyl propionate (50%) 1.0 part by weight (Propiofan ® 6 D,BASF AG) Water 4.5 parts by weight Sodium salt of a polyacrylic acid(40% in water) 0.5 part by weight (Indunal ® NKS, Indulor Chemie) Nasalt of a sulfosuccinic acid ester (Lumiten ® 1.0 part by weight IRA,BASF AG) Mixture of fatty acid, polyglycol derivatives and 1.0 part byweight hydrocarbons (Dehydran ® 1227) Titanium dioxide (rutile)(Finntitan RDD, 50.0 parts by weight Kemira, Finland) Sodium aluminiumsilicate (Ketjensil SM 405, 2.0 parts by weight Akzo-Chemie) 100.0 partsby weight

For Forming the Layer of Pressure-sensitive Adhesive

Aqueous acrylate dispersion (50%) (Freihoff- 65.0 parts by weightDispersion VP 859/6, Freihoff-Chemie) 25% aqueous ammonia solution 1.5parts by weight Na salt of a sulfosuccinic acid ester (Lumiten ® 1.0part by weight IRA of BASF AG) Water 32.5 parts by weight 100.0 parts byweight

The above dispersion for forming the cationic layer is knife-coated in aquantity of 10 g/m² onto a 50 μm thick siliconized paper support. Thewater is then evaporated off at around 100° C. by passing warm air over.The aqueous dispersion for forming the anionic layer is thenknife-coated in the same way onto the surface of the already formedcationic layer and the water is subsequently evaporated therefrom. Thelayer of pressure-sensitive adhesive is then formed on this layercombination by applying the aqueous dispersion described above in aquantity of 5 g/m². The water is evaporated off as described above.

EXAMPLE 2

The procedure is as described in Example 1 except that the followingformulation is used to form the anionic layer.

Aqueous copolymer dispersion of n-butyl acrylate 30.0 parts by weightand styrene (45%) (Acronal ® S 725, BASF AG) Aqueous carboxyfunctionalacrylate copolymer 10.0 parts by weight (69%) (Acronal ® V 205, BASF AG)Aqueous polyvinyl propionate (50%) 1.0 part by weight (Propiofan ® 6 D,BASF AG) Water 4.0 parts by weight Sodium salt of a polyacrylic acid(40% in water) 0.5 part by weight (Indunal ® NKS, Indulor Chemie) Nasalt of a sulfosuccinic acid ester (Lumiten ® 1.0 part by weight IRA,BASF AG) Mixture of fatty acid, polyglycol derivatives and 1.0 part byweight hydrocarbons (Dehydran ® 1227) Titanium dioxide (rutile)(Finntitan RDD, 50.0 parts by weight Kemira, Finland) Sodium aluminiumsilicate (Ketjensil SM 405, 2.0 parts by weight Akzo-Chemie) Aqueousaluminium paste (65% (Aquasilber LPW 0.5 part by weight 1380, SchlenkAG) 100.0 parts by weight

A This dispersion is used instead of the dispersion of Example 1 withwhich the anionic transfer layer was formed. The formulation is designedto be tacky so that there is no need here to form a layer ofpressure-sensitive adhesive, as in Example 1. The dispersion is appliedin a quantity of 10 g/m².

EXAMPLE 3

Example 1 is repeated with the modification that the dispersiondescribed there for forming the layer of pressure-sensitive adhesive isreplaced by the following formulation.

Aqueous acrylate dispersion (50%) (Freihoff- 65.0 parts by weightDispersion VP 859/6, Freihoff-Chemie) Aluminium paste (65%) (AquasilberLPW 1380, 2.0 parts by weight Schlenk AG) 25% aqueous ammonia solution1.5 parts by weight Na salt of a sulfosuccinic acid ester (Lumiten ® 1.0part by weight IRA of BASF AG) Water 30.5 parts by weight 100.0 parts byweight

This formulation is knife-coated onto the anionic transfer layer formedbeforehand in a quantity of 5 g/m² by the same procedure as described inExample 1.

What is claimed is:
 1. A multi-layer flexible transfer tape comprising abacking, a layer of pressure-sensitive adhesive, and twobinder-containing pigmented transfer layers, which are different fromthe layer of pressure sensitive adhesive, wherein at least onebinder-containing pigmented transfer layers are present between thebacking and the layer of pressure-sensitive adhesive, one of thebinder-containing pigmented transfer layers is cationic, and one of thebinder-containing pigmented transfer layers is anionic.
 2. Themulti-layer flexible transfer tape of claim 1 wherein each of thebinder-containing pigmented transfer layers has a thickness of about 5to about 25 g/m² and the total thickness of the binder-containingpigmented transfer layers is about 15 to about 30 g/m².
 3. Themulti-layer flexible transfer tape of claim 1 wherein the adhesive layerhas a thickness of about 1 to about 5 g/m².
 4. The multi-layer flexibletransfer tape of claim 1 wherein a fine particle metal powder is presentin one or both of the anionic binder-containing pigmented transfer layerand the adhesive layer.
 5. The multi-layer flexible transfer tape ofclaim 4 wherein the fine particle metal powder is comprised of aluminum.6. The multi-layer flexible transfer tape of claim 4 wherein the fineparticle metal powder is present in the form of platelets.
 7. Themulti-layer flexible transfer tape of claim 6 wherein the platelets havea thickness of about 3 to about 10 μm and a diameter of about 4 to about1 7 μm.
 8. The multi-layer flexible transfer tape of claim 4 wherein thefine particle metal powder comprises about 0.1 to about 3.5% by weightof the anionic binder-containing pigmented transfer layer or adhesivelayer in which the fine particle metal powder is present.
 9. Themulti-layer flexible transfer tape of claim 1 wherein the anionicbinder-containing pigmented transfer layer is located between thecationic binder-containing pigmented transfer layer and the adhesivelayer.
 10. A multi-layer flexible transfer tape comprising (a) abacking; (b) an anionic binder-containing pigmented transfer layerhaving a thickness of about 5 g/m² to about 25 g/m²; (c) a cationicbinder-containing pigmented transfer layer having a thickness of about 5g/m² to about 25 g/m²; and (d) a pressure-sensitive adhesive layerhaving a thickness of about 1 g/m² to about 5 g/m²; wherein the cationicbinder-containing pigmented transfer layer is located between thebacking and the anionic binder-containing pigmented transfer layer andthe anionic binder-containing pigmented transfer layer is locatedbetween the cationic binder-containing pigmented transfer layer and thepressure-sensitive adhesive layer.
 11. The multi-layer flexible transfertape of claim 10 wherein about 0.1 to about 3.5% by weight of fineparticle metal powder comprised of aluminum is present in one or both ofthe anionic binder-containing pigmented transfer layer and thepressure-sensitive adhesive layer.
 12. The multi-layer flexible transfertape of claim 11 wherein the fine particle metal powder is in the formof platelets having a thickness of about 3 to about 10 μm and a diameterof about 4 to about 17 μm.